Telephone system.



F. W. DUNBAR.

TELEPHONE SYSTEM.

APPLIGATION TILED o01'.11,19os;

1,133,1 13. Patented Mar. 23, 1915.

7 SHEETS-SHEET 1.

snoupa v 11176805 P. W. DUNBAR. TELEPHONE SYSTEM.

urmoumn run our. 11, 1906.

Patented Mar. 23, 1915.

w SHEETS-SHEET 2.'

- a 12 WE J 1 WM UZZZQZgz /f F. W. DUNBAR.

TELBPFWB SYSTEM.

7 APPLIOATIOK IILED OCT. 11, 1906. 1,133,1 13. Patented Mar. 23, 1915.

7 BHEBTS-SHBET 3.

F. W. DUN BAR.

TELEPHONE SYSTEM.

APPLICATION FILED OUT. 11,1906 1,1 33,1 1 3. Patented Mar. 23, 1915.

'1 SHEETS-SHEET 4.

F. W. DUNBAR.

TELEPHONE SYSTEM.

nrucuxon rum) 0GT.11,1906.

Patented Mar. 23, 1915.

7 SHEETS-SHEET 5.

p .r w II In v Q; iv .21 i

F. W. DUNBAR.

TELEPHONE SYSTEM.

APPLIOATIOR nun 00T.11,1906.

Patented Mar. 23, 1915.

7 SHEETS-SHEET 6.

1?. W. DUNBAR. TELEPHONE SYSTEM.

APPLICATION FILED 00111, 1906. r 1,1 33,1 1 3. Patented Mar. 23, 1915.

7 SHEBTHEBET l.

v To all whom it may concern folfowing'is as UNITED STATES PATENT OFFICE.

M615 DUHBAB, OF CHICAGO, ILLINGIS, ASSIGNGR. BY MESNE ASSIGNMENTS, TO

- KELLOGG SWITCHBOABID & SU'PPLY A CORPORATION OF ILLINOIS.

TELEPHOIFE SYSTEM.

Specification of Letters Patent. h Pat nt d )I 23 1915 Y Apgrlicationfiledfletobcr 11,1906. Seria1Nm338A17.

ipea uredff pay-station and slot machine" service-mm)? be bandied in a uniform mamier by the caH recen'ing operators, and whereby the correct data upon which charges zgre based, maybe auromat-ically iegastereiigor the deposited coins automatically Be it'known that I, F RANCIS W. Dmzmr. a eitimn'of the United States, and resident of Ghicago, county of Cook, 'and State of have invented new and useful Improrements in Teiephooe Systems, of which n 3? inventioh to-telephone inother ifegrture t-onsists in the provision The present 7 I ex systems and more porof means whereby the business originating crrit-temrinaiing in a plug! or in othergijmnnorder from the caning subscriber letters Iatentjfiled hereioiorey Inone my grid applications, I knife proyided'sfel r ice rixet er s'intfiri'd mritoirhesizbseribierlines I adapted to airtomilfically eonnt oompletwlr-q eaflul for connections; In my present n-ntio'm'l provide-1 grail}: of service re wifhich the subscribers calls are automatihis line either directlftrith the-lined completed caiiodior connections imam? 1b tielflgfly to-that oieuch systems in foamy erficuiargzmlp of lines may be distnhnteg mnong a pluralityof groups of switches thereby makine nniform the originating bu siness handler? by each group, of

eally'distribiited before various operators at the central oflice in a predeterminedorder.

In switch at "the central ofiice, set in motion by the remorzil of the coiling partys receiver its'hook, mama i au tomatieolly estahiisheg connection beinother featme consists in providing tween the calling line, andvenidieJink-cir- I for interconnecting subscribers. lines pra (fed. with inciiridl-lrl answering termi- .mfisf lines ki'ided witii means for selecting idle linkcircuits and ng [means :for readiiy changing from "one ciass of service tom;-

witehes ia xd.; see ring thehighest efiieiency om the mstniied automatic selecting apzrilj jopeiteitl "eonneering before gm operator, and extends a (211i sigr al thereto. The operator thereufion may-"receive the the ageneyofher telepholie set dee -er i 1 r V comprises still other then be eonnecteti to the like of rhegri ed h pre ier? r H.

fl e 'syste nsofnatiirejtlsembetlin n'gfr nifhe employ- Qse .er'ai ofmy-219p icationsfm-efinited"States err-iron mi? be more full;

M n-mm to ri e following p on taken ineounection with awings. and the'scope of v a .rinres of the invention will be za iimrehf from time appended riaims. while the, more \spifliifie fea tii-im haw 11g been diistm's for a larger group ofs'u bseribem rifled o' ti iviilfbe oiiide the subject matter fines. Thus, ten of said, registersvmay be of flirismnaiapplications provided for :rlgrnupofone hnnihfetllines In like (h'znving. Figure l romprlszng am! wvili'conjoinfly automation register g'azrrts. 11 ':2,fiil.:|str: tes-rliogrmnmmtiraHy niw DE'GfiFHBdjaliziflgem flli of the 5Uil-ffltib0r eirciiits in? seieE-iingsnvitcixes applied to mieweli kmmu {rpe oftelepimne exchange system: Fig. I illustrates dingm mnaticaiiy nrie msition-of the romacts of l min-hmor pay-station apparatus: Fig. 2 iliustrntm diagmimnatiehiiya preferred or: angenwnt emof the said one hundredsubscriliers.

lumber fezitm'eof my present im'entic m r'QiLiifgi in providing means for antouiilti mil railleeting a coin or f token deposited in a win-Ming; snbscribers set. upon the e-mnpirtinirmf the desired connection and for fn liton mtically returning Said 'eoin 01: {of the-opel 'atofslink-circuit in hicir party flgoken"? II] case the desirul'subsoriimr be line selective s gnalmg men-hams 15 emyl pioyed': Fig; 3 'iiiusirntes z: modmed imk Another' from" of my in'rentimi consists Fig i iiiustrnies ilin m thfeprovision of means whereby the various classes of se!'\'1'ce-such as unlimited."

eireuit "or :mgemeni;

switches which may be used in place of the corresponding similar arrangements of Fig. 1; Fig.- 5 illustrates diagrammatically an operators circuit for use in placing two parties on the same party-line in communication with each other; Fig. 6 illustrates diagrammatically a trunk circuit adapted to interconnect subscribers in different cen tral oflice's; Fig. 7 illustrates diagrammati cally one arrangement of subscribers circuits for securing interconnection between subscribers having individual answering terminals and those rovided with means for automatically ecting idle link-circuis; Fig. 8 illustrates diagammatically a link-circuit for completing connections when calls an? received over individualanswering terminals illustrated in Fig. 7; Fig. 9 isia front elevation, partially cut away, of a link-circuit selector switch of the character dia atically illustrated in Fig. 1; Fi 10 is a side elevation of the same switc viewed from the ht; Fig. 11 is a partial vertical section of e same switch taken on the plane indicated by the line 8, 8, (Fig. 9) Fig. 12 is a detail of a pointer and scale associated with said selector switch; Fig. 13 is a diagram of the contacts adjacent to the zero position ofthe switch; Fig. 14 'm a side elevation of a er for use in the systems illustrated in Figs. 1 and 4; Figs. 15 and 16 are'detail views of the periphery of the type wheel and tape respectavcly of Fig. 14, and Fig. 17 is a front elevation of a coin-bog or paystation mechanism, the inclosing casing and coin chute bei shown in section.

A brief description of the arrangement of apparatus and circuits illustrated in Fi l and 2, is given as follows: The so lines are divided into groups, say, of one hundred The operators link-cireuitsare also preferably divided into groups of, say, one hundred each. Each group of one hundred link-circuits provides ample facilities for handling the originating calls from say fifteen hundred linesthat is, from fifteen groups of one hundred lines each, or perhaps from a larger number of groups, as it would seldom occur in practice that any group would be completely filled with operatively connected lines. I then provide a .proper number of pairs of selector switches for each group of lines, say, ten palm of such switches for each group of one hundred lines, one switch, H, of a pair I term a line selector and one, I, a link-circuit selector. If the lines and link-- circuits be thus grouped in hundreds, I preferably employ selector switches having one hundred operative stationary positions or points, each point .compr'ming the necasary number ofcontact members required for each line or link-circuit. is provided with'movable contact members or wipers, and two of the sa d wipers of a 'of subscriberslincs. 'Iprovideforj v I of an addit onal switch which Each switch pair of switches are electrically connected to complete the talking circuit. The conductors uniting the said movable wipers may be properly termed a link, an intermediate link or a link-circuit. each group of one hundred are multiply connected to the stationary points of the ten line selectors belonging to the group and the one hundred link-circuits are multiply connected to the stationary points of the link-circuit selectors of the entire fifteen groups, in the example chosen as an illus tration. It thirefore follows in the illustration assumed, that the one hundred linkcircuits will be multiplied one hundred and fifty times-that is. will be connected to one hundred and fifty link-circuit selectors, thus rendering their use common to fifteen groups of one hundred lines each.

As an example, assume an exchange consisting only of fifteen hundred subscribers lines, divided into fifteen groups of one hundred lines each. Each of said groups of lines would be provided with ten line selectors and ten link-circuit selectors, whereby each subscriber in the exchange would have access to any one of the one hundred link-circuits, although facilities are farnished. for establishing only ten simultane; ously' existing calling connections. in any group of onehnndred lines.

It wilLbe understood that my invention isnot limited in the number of pairs of switches which may be provided for the common use of a group of subscribers lines for calls, but that a snfiicient number of. pairsof such switches will be Provided to a omm d nd P per y die the originating business fromiaggrou suc , m. atm is er it h said master is for the common use of the. subscribers in its allotted grou and its function is, upon the initiation o a call by any subscriber in its group, to start the rotation of an idle pair of switches allotted to said group, whereby the line selector may select. and make connection with the calling subscriber, dud the link-circuit selector may select and make connection with the first idle link-circnit apportioned to the common use of the fiiteen groups of one hundred subscribers lines. The said master switch is not included in circuit with the completed connection, but on the contrary is freed the instant it has caused the line selector to ,con nect with a calling' subscriber, and will then move forward. In case there be at this time no other calling subscriber in the same g1 oup the said switch will stop in engagement with-the contact points of the next idle pair of selector switches. In case there be at this time another calling subscriber in the same group, the said master switch will The lines of immediately start a second pair of selector switches for the purpose of completing the connection between said 'siibscribers line and the next; idle link-circuit in the group apportioned to the said fifteen hundred lines, chosen as an illustration. It is apparent that if the exchange be limited to the said fifteen hundred lines, chosen as an example, each calling subscribcrs line will be automatically connected to the first idle link-circuit in the exchange. Suppose, however, that three thousand subscribers lines be connected with the single central ofiice now under consideration, thus, presumably, requiring two groups of one hundred linkcircuits each to handle'the originating business from each majorgroup of fifteen hundred lines; In this'caxy the subscribers would still be divided intominor groupsof,

say; one hundred lines each, and the link circuits for each of the two majorgroups would be preferably alternately terminated at each operators position,wsofthatlink-cin cuits 1, 3; 5, 1', etc, ofeachoperatoris position. would be accessible to; the first major group of fifteen hundred. linesand link-circuits 2, 4, 6, 8, etc, of each operators; position would be accessible to the second major group of fifteen hundred lines. In case forty-five hundred subscribers lines iverej led into the same exchange,thus requ ring,

in the example chosenpthree groupsjof one hundred link-circuits each, each operators position would be providedu ithlink-circuit terminals; of which each th n-d one m 115+ merical order, would be reremuy ac e ble to one only of the three H1310! groups of sumcribers liues. i In the present case I also prorrde whereby the number of operatrvely connected link-circuits terminating at each or any operators position maybe *:i ried at the discretion of a chief operator-ortrallfic man agcr or similar executive. In order'tojn'ef embly; provide the maximum firczl ltles "fut" each operators position lempl oy a grater number of linkcircuits'terminating at each operator s position than will be operatively required on the average. Eachlink-circuit is preferably proridcdwith a switch under the control of the said executive whereby its corresponding link-circuit may be tempt lnrily placed in an inactive or artificially busy condition. and whereby the said executive may apportion the number of operativel cminccu-d link-circuits terminating at each operator's position in accordance \iith the ellicienc of the operator then present at said position.

Referring now particularly to Fig. 1, three subscribers lines are indicated. each supposedly in a different group and ear-ll group preferably comprising subscribersof a separate servic" class. Thus the group including line is equipped with subscribers having limited or measured service; a charge being made for each completed connection, or for each completed connection in excess of a fixed number. Preferably each line is equipped with but one subscriber. Que such subscribers setis shown utBnnd consists of a well-known arrangement of apparatus, including hell 1, condenser 2, transmitter 3, receiver 4, book 5, and retardation coil 6. No further descrip tion-is required of this apparatus, nor is my invention limited to any particular type or aimangement of telephone set. The group including line 805 is equipped with subscribers having unlimited service, no charge other than the fixed service charge being made. Each line may be equipped with one or moresubscribers. Four such subscribers sets for line 805 .are shown at C, C, C,

and C. The sets maybe similar to those shown at B, except that Where several are included on the same line their bells are preferably adjusted to dilferent rates of cur- 113111;, so that they may be selectively signaled. Tl1us, 'for example, the four bells shown at 1 .may be tuned respectively to respond to twenty, forty, sixty and eighty alternations r second. The roup including line 5' is equipped with slot-service orcoin-box subscribers; a coin or token beingrequireddcposited for each call made. said coinbeing returned if the desired called line he busv and collected if connection be completedliach line may be equipped with one QI'JHOIG subscribers. Two of such subscribersfsets for line 5 are shown at A. Afiandtwoothers suggested at A, A. The

sets me [similar to those shown on lines 205 and 80:.w1th the exception of the added coin depositing and collecting device diagrammatically shown at l) and illustrated in mechanical detail in Fig. 17. The reta rdation coil 6 of the regular set is preferablyureplaced by a polm'ized relay 7 whose Winding isnormally extended to ground ia normal contacts of springs 9 and 10'. The position of the deposited coin is shown in:

thedolted llhlts in Fig. I while in Fig. l". the coin itself indicated bv the full liuc circle 10 As'sliown in said latter figure. tlzedcposit of'thc coir. will by its weight cause the pivoted arm 13 to depress conta t prings 1" and 9' so as to close contact and open contact 10' thereby interrupting the normal ground conection via lfl'.andexlemling the winding of relay? to the line limbl/ via 9. The (liagrummatically illustrated bifurcated pivoted arm ll arrests the armatureand limits its movement in either d rection. except when u l19u-'} current from :1 gpeqiul high pot ntial source of current 72 located at llw-rcntral ollice. is pusscd l'nrorgli the winding of relay 7' \Vben said current is passed through the relay in a direction to cause a complete upward attraction of its armature, the extension 12 of arm 11, which freely slides along the upright arm 13 pivoted to springs 10' and 9. will tilt the said arm 13 to the right, thus dropping the coin into the coin-box via chute 15. W'hen. however. said heavy current is passed in a contrary direction through the relay, the complete attraction of the armature in a downward direction will cause the arm 11 to tilt arm 13 to the left and return the coin to the Tia chute 14. A flow of current of the ordinary value from the regular low voltage talking common battery I) will cause the relay to attract its armature only silficiently to contact with 9 and open it from its normal ground contact, via 30.

- thus causi the same circuit changes as are caused by t e deposit of the coin. Current from the normally connected low voltage signaling battery 6., of reversed potential with res to b will cause the armature 8 tube elevated until stopped by the arm ll.

At the central oflioe, the subscribers hnes extend through a main distributing board diagrammatically shown at E, whereby the lines may be distributed to their multiple spring-jacks F in regular numerical order. Each line is provided with a cut-oil relay 16 and a line relay 19. A protective resistance 19' is preferablyemployed between the live pole of the battery 6 and its normal connection to the line. The extensions of the line wires and the conductors extending to the line relays are preferably carried through an intermediate distributing board G, whereby any line may be extended to any group of selector switches without alter lag the number of the subscribers line or multiple spring-jacks. Thus suppose subscriber 205 desires'to change the character of his service. say, from measured to unlimited. The short jumper wires 9 may be re-run to connect his line with a different group of selector switchs comprising unlimited service subscribers. without altering the connection to his multiple jacks or changing his ca e number. Similarly. the intermediate distributing board G may be utilized for regulating the number of subscribers connected to a given cup of switches and for regulating the on originuting in any group of switches. Thus it will necessarily happen that certain groups of lines originate more calls than other groups unless the grouping arranged with reference to the average business actually transacted. The intermediate distributing board atlords facilities, by the rerunning of the said jumper wires 9, for thus equalizing ti'ie orig'nating calls in the "anous groups.

In I. the three lines are indicated as belonging to three separate groups arranged according to the classes of business; each group being provided with a plurality of line selectors H. H, etc. suflicientin number to handle the originating calls of the group. I. I, etc.. are the correspond ing link-circuit selectors; I being the mate of H: I the mate of H. etc. Selectors H, I, are indicated in full with their associated relays and switching mechanism, whereas H, I, are only partially shown. Conductors T, S and L represent the conductors extending to the link-circuits at the operators positions. each complete link-circuit comprising a conductor T, a conductor S and a. .conductor L. As previously described, these conductors are multiply connected to the various stationary points of all the linkcircuit selector switches I. I, etc of a major group of lines. J represents diagrammatically an intermediate distributing board through which the link-circuit conductors are extended and by means of which the said link-circuits may be variously distributed to the operators positions. The distribution is preferably such .tlrat the manuallyoperated terminals of the various link-circuits occur in the same numerical order at the switchboard as on the stationarjr contacts of the link-circuit selector switches, the first point of the link selector switch being carried to the first link-circuit terminal, the second point to the second terminal etc, when there exists but one group of lint-circuits. If there be a plurality of grou s of link-circuits. then the distribution would preferably be that heretofore described wherein each operators position is provided with link-circuit terminals accessible to each major group of lines, and in which said link-circuit terminals of each group occur in the same numerical order at the switchboard as on thestationar'y contacts of the link-circuit selectors. Furthermore, instead of having this equal distribution of link-circuits for each group at each operators position. I may by means of the jumpers of the said distributing board J, distribute thel'Enli-circuits corresponding to any major group of subscribers line. unequally in any preferred manner. before the different operators. For example, it may happen that one particular major group of fifteen hundred lines originates the greater part of the calls during a certain period of the night. It would therefore be preferable to provide the first operators position with a greater number of link-circuits accessible to this particular gruup-und with fewer .link-circuits 'from th other groups; thereby enabling one operator to handle all calls from that group from one position. It thus appears that through the agency of the various distributing menus above described. I am able to equalize the load among the various groups of selector switches. whereby the greatest efficiency of the installed apparatus is obtained. and am able to most t, s. and

ef'ficientl distribute the load among the various groups of link-circuits and at the \u- Pious operators" positii us.

Each group of subscribers lines is provided with a master switch K, the said switch hn in preferably as many stationary contact points as there are pairs of selector switches. or even multiples thereof, in the group. Each point is electrically asso ciated with its corresponding pair of selector switches. The selector switches are diagrammatically illustrated in Fig. 1. As tlieicin shown, the line selector comprises a shaft 21 capable of being rotated step-b5- step by the magiet 21 driving the ratchetwheel f xed to said shaft; the said shaft carrying a o. the insulatedwipers 23, 24. adapte to contact with fixed contacts multiply cimnccted to the line conductors in addition, the shaft carries apointer: :6, bearing a fixed relation to the said wipers andrototing over agraduated dial. the graduations corresponding to the fixed contact points of the switch and'being preferably num ered in numerical order from 1 to 100. The line wlectors provided for groups of lines containing meastired or limitedservice subscribers are pro- 'ided with a printing mechanism or register )1. This register is shown in detail Fig. 1i. but may be described as consisting essentielly of a type'whccl QT-fixed'to the same shaft 21' carrying the wiper-sand pointer: said type-wheel being preferably provided with removable type-plates carrying-Ilium hers corresponding to tlie subscribcrs lines,

and occupying positions corresponding to- 28 is the printing magoet'n liich, onflthe attraction of its crmature' 29; courses the hammer 30 to print tlieopposing number on the paper strip '31 carried between the type and; hammer; said paper strip being unrolld from bobbin 31 and rolled up on bobbin The rev-action of thc utmature'i'il will drive Elle ratchet-wheel one tooth in the direction -{urn-l3}: the arrow so as to unwind the papal-from one bobbin and Wind on the other bobbin, thus bringing a nor: space lhstn'een the hammer and the lypswlicel.

The link-ciicuit selectors are essentially of the same (:0 Each link-c rcuit selector is adapted, howererto automatically return to its normal or zero position at the time of release, and position he insulated projection 34,

bf? the evolving shaft 21, is adapted 1;-

i n Contact springs In the case of the c .lE-IJUIES I. I. etc. in groups 1 and the projection 34 in its normal position closes; contact 3-) and opens contact 36 'liiic in em but the normal or zero posi- QJI . Several ructien as the line selectors.

selectors of group 2, the contact springs 35', 36. 37 and 38 are raised so that contacts 35' and 36' are closed While contacts 37' and 38' are opened. In any but the normal or zero position, contacts 35' and 36' are open and contacts 37' and 38' are closed. A pointer 26 may be also supplied to the linkcircuit selectors, if desired. Likewise the master-switches are of practically the same construction as the other selector switches. Each master-switch is provided with a Stepby-step magnet 21 actuating aratchet wheel 22' fixed to a Shaft 22 which carries wipers 57, 56 and 'zi'8 clectrical'ly insulated from each other and adapted to make connection with the fixed contacts, respectively asso- 'ciated with, and electrically connected to,

box subscribers station set.

6* represents a source of current of the same polarityes 7*, but of lower potential.

5 represents 1 source-of current of relatively low potential with respect to b, but baring its opposite pole. grounded It will be understood that eacnof the several batteries marked fbf may be, and preferably are, oneland thesumefbattery,.and the same statement, isjtrue with respect to the various batteries 5: and! true also with respect to the representsfn souroe of pulsating'or ntcrnat ing currcnrtov which magnets 21 and 21 ale responsive itwill be understood that. one such source may be employed for all of theseparate sources diagrammatically illustrated. The arrangement of: circuits ondyapparat-us asociat ed with the 'intermediate link electricully uniting a pair of selector switches is substantially the same '7 m each of (tie three groups of lines indicated. -d|fifering however in certain minor points which will be described later on.

X represents a busy back source of current and is adapted to give a characteristic signal to a calling subscriber if the'line for which liacalls is busy. It may consist of a variable source of current 37 curried through an interrupter 38 and the primary of induction coil 39; the secondary of said induction coil being led to condensers 40, one such condenser being preferably provided for eachpair-of selector switches.

0 represents a signal-preferably of ,incandcscent lampu'hicb will be continuously lighted under certain conditions of trouble to gire a visual indication 01! such trouble to an attendant Each pair of senumber of the subscribers line on which trouble'may exist.

I (Fig. 2) diagrammatically indicates a party line selective ringing key, whose oper- :ltion may be described as follows: 1:, p, p, p, represent the four ringing buttons which, when completely :lepre ed, are adapted respectively to extend ringing current from the corresponding; generator Q- ria resistance lamp Q to the alternate contact 41' of relay 41. Each button has two positions in addi-. tion to ilb' no mal position. In its-fully depressed position, the interrupter R is electrically connected to the winding of relay ll contact 4-2. The button is retained in its fully depressed position by an associated beveled stop -13 can-led by. :1 bar 4 5, and is retained in such position until said stop is withdri wn. As the button is depressed, the end of the lever adjacent to the stop shps o er the beveled-face of the stop into engagement with its opposite face Upon the energization of the magnet 44, its armature l5 and the connected bar 46 are drawn downward to remove the stops 43 their engaging positions, whereupon the previously depressed lever will return to its intermediate indicating "position. It is held in its intermediate position bythe engagement of stops 49 and 50. 'The stop 49 is by a pin 47 secured to the armatureand it remains in its engaging posinon so long as the said nrmnture remains in its attracted position. As SOOIklIOKSBK-Gl', as the magnet- 44 is its annnture 45 returns to the position illustrnted and the stop 49 is moved from its engaging position, thereby allowing the actuated-key and its lever to return to, normlzl. From this descriptlon, it will be seen Lhatthe depression of any button will, by the engagement of its lever with ifs associated stop l3, more the bar 46 so as to more other stops 43 out of engaging position and thereby release other buttons which have. been previously de- U-represents a counter adapted to record completed connections. Each link-circuit lnav be provided with such a counter.

51 represents the counting ma net which, when energized, will cause tlle ratchetwheel-12 to make one step and, by a suitable in the opposite direction when inserted into the jack of an idle line.

1' is a switch preferably placed before the manager or chief operator, there being preferably one such switch for each linkcircuit. Each switch, when in its normal position (that shown), permits the selection of the corresponding link-circuit; but when the said switch is moved to its alternate or grounded position, the corresponding link-circuit is rendered incapable of selection by calling subscribers,in other words, is rendered artificially busy. Switches Y-tllliS supplement the functions of the dissributing board J by providing ready and rapid means for distributing the loada'mon'g the operators positions and for proportiohing the 11mm of calls received at any position in accordance with the ability of the operator then present at the position. As an example, the operator at the first position may be highly skilled while the operator at the second position may be less skilled and capable of handling efiiciently; only a relatively small number of calls. The trafiig manager or chief operator may then by means of the switches Y renderartificinlly busy all link-circuits at positions'in excess of: the number capable of being ciliciently' handled. When all operatively connected link-circuits at these two positions are in use, the calls will of course pass onto the third or subsequent posit-ions and the business at these positions may be similarly regulated by the switches Y. It is apparent thatin the event of a sudden or unexpected rush of business, which would otherwise extend calls to positions beyond the last one, at which. an operator is then present. the said manager may by the manipulation of the switches Y, place one or more of the artificially busy link-circuits at. one or more operators positions, in service, thereby distributing the unexpected additional load among the operators For .the purpose of indicating to the said monager the existence of this unexpected load suitable indica ing means are provided which may be efersbly located at his desk and which preferably consist of the lamps 95 one for each operators position, connected betweenbattery b and the armature contact of the pilot call relay 95. Said relay 95 is necessarily energized whenever a call extends to the operators position at which itis located. Therefore whenever manual switch 9.3" (preferably also under the control of the said manager) is closed and said relay 95 energized, lamp 95 will be lighted. By means of the several switches 95* the lamps 95 corresponding to the positions at which operators are present may be cut-out, while the remaining lamps 9 are left in circuit. Under these circumstances, calls which may be extended to upel".

ators positions beyond those at which operators are present. will be at once indicated to the manager, whereupon he may. as above described. distribute this additional unexpected load among the present operators.

Z represents a busy back jack. of which several may preferably be provided at each operatofs position. It is used for the purpose of permitting the release of selected link-circuit either when trouble exists upon the ailecting line or when it is desired to restore a deposited coin or token to a calling subscriber who cannot secure connection to his desired party. In either event the plug X is inserted. by the operator, into the said iack Z. I

Having pointed out the essential characteristics of the principal apparatus employed in establishing connection, I will now trace in detail the operation of the apparatus of my invention as illustrated in Figs. 1 and 2, assuming one of the subscribers on line 5 desires a,oonnection with some other subscriber in-the exchange. Referring first to the master-switch K of group I, it will be noted that whenever the magnet is energized, circuit will be completed through the motor magnet 21 and the master-switch will advance. It is also true that magnet 55 will be energized whenever wiper 56 is in engagement with a con tact point associated with 21 bn intermediate link as will appear from slihsequent de .scription. It necessarily follows, therefore,

that the wiper 56 {and consequently wipers 57 and 58) will be normally at rest and in engagement with contacts extending to an idle pairof selector switches. I will assume that subscriber A removes his receiver 4 from its book fonthe purpose of initiating a call- I will also assume that the said subscriber neglects to deposit a'coin. The 'remoral of his telephone from its book, therefore, merely includes battery 5 in closed circuit with protective resistance 19, line limb I transmitter 3, polarized relay and contaets 9 10', to ground and the return side of battery 6. The resulting flow of current is of a direction and potential to cause armature 8 to be merely elevated until stopped by arm 11. Consequently. no operative signaling mechanism is ailccted. In other words, the subscriber is unable to make a call until he has deposited a coin. Upon the deposit of a coin, however, arm 13 causes contact 10 to-open and i) to close, to include battery 6 in closed circuit via 19', L, 3, 7, 9, L and line relay 19 to the grounded terminal of the said battery 6; whereby the line relav 19' is energized to remove the ground In conductor 1 of line and to establish a flow of current from ground via armature spring 20 and its alternate contact, conductor 59, (common to thc' subgroup of one hundred subscribers), relay of the master-switch of that group, to battery 6'. Relay 60 is thus energized and would be energized via the same common conductor 59, were any other subscriber in the same sub-group to remove his telephone from its hook and deposit a coin for the purpose of making a. call. The encrgization of relay 60 locks its own circuit via alternate contact of siring 61 and normal contact of spring 62, thus preventing the denergization of said relay 60 until relay 55 is encrgized. In addition, the cnergization of relay 60 extends the ground connection via spring 63 through normal contact of spring 65, wi r 58, normal contact 35, normal conztact 0 spring 67, through private relay 68 to battery 6'. Relay 68 is thus energized to cause the operation of link-circuit selector magnet 21 from source 9, said magnet 21, contact 69, contact 70 to ground. Simultaneously spring 64 is closed to ground, completing circuit through contact 66, wiper 57, contact 71 and private magnet 72 to bat-i fiery b. The euergization of relay 72 may or may not complete the circuit of the stepby-step magnet '21 of fthe line selector H, depending upon the position of the local wiper 23 of said selector switch. It may happen that the-line selector H, when last used, had left its wipers (23, 24, 25) in engagement with the contacts of the line now calling. This, however, isan exceptional condition and would result in preventing any further movement of the said wipers, as will presently appear, because they are already in engagement with the contacts of the calling line. Reverting to the further conditions established by the energization of relay 68, it will be seen that the circuit of the intermediate link t, s", will be opened at springs 73, 74, and that the local wiper 75 of the link-circuit selector will be extended via alternate contact of ring 76, normal contact of spring 77 to sa' d relay 68, whereby the energization of the said relay 68 is placed under the control of said wiper 75 as soon as the normally closed contact 35 is opened by the first step of the motor magnet '21 of the said link-circuit selector I. In other words, the private relay 68 is initially energized via viper 58 of the masterswitch K and normal contact but its continued energization is dependent-upon ground-colinections via wiper 75 after the first step of said link-circuit selector I. After the first step of wiper T5 which is preferably provided with an enlarged contact member capable of bridging from one stationary contact point to anosaer so as not to interrupt the circuit established there through in its passage from one grounded contact to another). relay 68 will only remain energized as long as said wiper encounters contact points connected with local conductors L of link-circuits then grounded. It will subsequently appear that local conductor L of each link-circuit will be either directly grounded or grounded through a battery I) of reversed potential (an effective ground) at all times when the said link-circuit is busy. W'hen, however, the said wiper 7 5 encounters a contact int connected with a local conductor L an idle link-circuit, the circuit through relay 68 will be entirely opened. This will appear on referring to Figs. 2 and 3, which re resent the normal or idle condition of 2.- HB -circuit. Conductor L is normally extended via spring 78 to switch Y. Said switch in its normal position is free from ground. Therefore, if said link-circuit be both idle and in a condition to be selected (that is, if switch Y be in its normal position and not thrown to ground), relay 68 will be deenergized, thereby interrupting the current through motor magnet 21 and continuing the intermediate link t 8, via wipers '1' 9 and 80 to the link-.

circuit conductors T, S. The opening of the circuit of magnet '21 revents the further operation of the link-circuit selector switch. Meanwhile, the line selector switch H has been selecting the calling subscriber's line (unless its wipers were already in engagement therewith).

It' will be noticed that the circuit of the step-by-step magnet 21'of line selector H can only be initially closed by the simultaneous energization of relays 72 and 81; its

- circuit being normally open at 85 and 86.

Relay 81 may be termed an oil-normal relay because it can only be energized when the corresponding link-circuit selector I is 1 off its normal or zero point, thereby closing circuit from battery through said relay 81 and'contact 36 to ground, thus causing the energization of said'relay 81 as lon as the switch I remains oil-normal. he first step of the linkcircuit selector I will necessarily energize said relay 81. Relay 7:2 (initially energized via 71. 57, 66 and 64) 'will be released simultaneously with the energization of relay S1, unlem a ground be then present upon the conductor 1 then in engagement with wiper If the said wiper '23 be then in engagement with the conductor 1 of the calling line, no such ground will be present, for spring of line relay 19 is then in engagement with its alternate contact. Therefore, the step-by-step magnet '21 cannot be energized and no movement of the line selector switch H will take place. The more general case, however, results when the wipers 23, 24, '25 are not resting on the contacts of the calling subscribers line. In such case, the initial nergization of pri ate relay 72 locks the said relay via alternate contact 82, conductor l, wiper 23 and normal contact 20 of the relay 19 of that line then engaged by wiper 23, to

ground. Relay 72 therefore remains energized after the energization of relay 81 and thereby causes the energization and operation of motor magnet '21 of line selector H, until wiper 23 encounters a conductor 1 not connected to ground-i. 0., until the wipers 24, encounter the conductors l, s, t, of a calling line. Relay 72 will then be deenergized and will open the circuit of 21 to prevent further movement of the line selectoi'. During the rotation of the said line selector H, the wipers '24, were electrically opened at 83, 84. Wipers 23 of the line selectors H, H, etc, are also preferably provided with contact faces capable of ridging from one contact point to another. It has appeared that the closure of contacts 63, 64 of the master-switch caused the operation of both selectors of the idle pair then engaged by said master-switch, to cause, on the one hand, the selection of the first idle link-circuit and, on the other hand, the selection of the calling subscribers line; also that the denergization'of the private relays G8 and 72 unites the calling line with the selec'ted link-circuit via the intermediate link' t, s. It is also 'apparent that as both selector switches H, I, are started practically, simultaneously, each to seek out a certain circuit, either one may first complete the so lection. For example, during the idle hours of the day, the probabilities are that the link-circuit selector I will onthe are first complete its selection; but during e busiest hours of the. day, the probabilities are that the line selector will on the e 'crag'e first complete its selection. -While both selectors are in motiongrboth sets of contacts 83, 84, and 73,74areon open circuit. Should H complete its selection prior to 1, thereby closing contacts 83. 84' before T3, 74, it will line 5 busy. The instant however, relay 68 is released, upon the selection of the first idle link-circuit, circuit from battery b will be closed simultaneously through relays 89 and 90 (Fig. 2), via 89, S, 80, 74, s, 24, 8, 17, L, substation A, L, t. t, 73, 79, T, 90 to ground; whereby both of said relays 8.) and 90 will be simultaneously energized and will immediately ground conductor L (Fig. 2) via alternate contact 78, normal contact 91, normal contact 92 and alternate contact 93. On the contrary assumption that the link-circuit selector I completes its selection prior to the line selector H, it will be seen 5 via relay 89 (Fig. 2), S, 80, 74, a, 24, s and saidrelay 16 to ground, prior to the extension of the circuit through the substation and relay 90 (Fig. 2), S, 80, 74., s, 24,

s and said relay 16 to ground, prior to .the

0. extension or the circuit through the substetion and relay 90 (Fig. 2), above traced. Should, therefore, relay 89 be so adjusted as to close alternate contact 78 prior to the opening of normal contact 94 of relay 90, it would close battery 6' (Fig. 2) to conductor L,'via pilot relay 95, calllamp 96, normal contacts 94, 92, 91, and alternate mntaet 78; but the said conductor L is then closed to ground via 75, normal loontact 76, 76', conductor 76, wiper 58, norinalcontact 65 and alternate contact 63, whereby the polarized relay 97 is short circuited and thereby deprived of current which would otherwise flow through it and cause its operation at this time. Upon either assumption, therefore, with respect to the order of complete selection by switches H and I, it is apparent that conductor L will be grounded to prevent the operation of the relay 97 and to prevent any other selector irom stopping in enga t with the link-circuit now selected an consequently busy.

' Upon the'operation of the cut-oh relay 16 (which, as we have sum, will be operated the moment the line selector H has selected he subscriber), it is ap ment that the disconnection of the line re ay 19 will result in the restablishment of the ound on 1, whereby a circuit is comple from ttery b',.via'relay'55 of master-switch K, ts wiper 56, contact 8, normal contact 82,

nductor ig'fiiper 23,1ronnal contact 20, to ground; thereby operating said relay to unlock relay and to energiie the motor magnet 21 via alternate contact 62 to ground. The mastergswitch thus advances one step, thus bringing wiper 56 into engagement with the next pair of selector switches in its group. Should this pair be busy, ground would be present on the conductor 190 either at a contact 20 of a calling line vizfcontacts 98, 82, conductorl', wiper23, conductor I and norma contact 20, or, in case the parts were then being restored to normal, ground would be present at contact 101, (as will later on appear) ;thus causing in either case the continued attraction of relay 55 and advance of the masterswitch, until an idle pair of switches is encountered; at which time, conductor 100 beopen, relay 55 will be denergized and cause the master-switch to stop in en t with the said idle pair of switches. H rotation, the circuits of wipers 57,

58, are open at 66, 65, respectively. If there had been at this time more than one calling subscriber in the group containing line 5 then, as above described, relay 55 would cause the advance of the master-switch to the next idle pair of switches, and upon the denergization of 55 (relay 60 being now energized by the second or simultaneously calling subscriber), the said idle pair of switches would be started to pick up the calling subscriber in the manner set forth above; and upon the selection of the said calling line, (entirely irrespective of whether or not the correspondin link-circuit selector has previously seected the link-circuit), the master-switch would again advance and finally come to rest in engagement with an idle pair of selector switches after attending to all calls then being initiated in its group. The master-switch, therefore, is normallyin engagement withan idle pair of selector switches, as previously stated. It is also apparent that the step ping forward of the master-switch has removed the previously existing short circuit of relay 97 via conductor 76, wiper 58, contacts and 63, to ground;- wherebysaid relay 97 is now operatively connected to the conductor L extending to the link-circuit and will respond to current which'will at a later time be sent back over said conductor L. Relays 89 and 90 (Fig. 2), being now energized, close circuit from battery 6', through pilot relay 95, call lamp 96, alternate contact 94 and normal contact 102 to ground, thus lighting said call lamp 96 to advise the operator that a subscriber is awaiting attention on this particular linkcircuit. Pilot call lamp 95' is simultaneously lighted for the well-known purpose of supplying a pilot call signal common to all the linkcircuits at the operators position. If at this time switch 95 be closed, lamp 955 will be also l ghted for the purpose previously described. The indicates the common point of the group of link-circuits. The operator now communicates with the calling subscriber and finds out his wants by the use of the well known apparatus indicated at V, o, o. Returning to the substation A', it is apparent that the reversal of current through the relay 7 at the time battery b was included in circuit with relays S9 and 90 has merely altered the posi- -tion of armature 8 without altering the effective electrical connections. ing

the subscriber desires a line in the same ex-- change, (all which lines I preferably provide with multiple spring-jacks F), the op erator will preferably first depress a button p of the selective ringing key -P. corresponding to the adjustment of the bell of the party on the line desired (whether said line he an individual or a party line!) and will then insert plugX into a jack car respondin to the line of the subscriber desired, wit iout first testing said jack. The depression of any ringing button p establishes a flow of current from battery I), through relay 41, contact 4'. of said ringing button 72, through the common interrupter R to ground, whereby said relay 41 is intermittently energized and deiincrgized to cause its armature l1 to alternately contact with its normal and alternate contacts. Depending upon whether said line is idle or busy, or whether or not the subscriber answers, three conditions arise which will be separately discussed. 0

First, called subscribers Zine idle.In this case, the sleeve rings f of the jacks F will be at the potential of ground, for'each such ring is connected thereto via cut olf relay 16 without connection to battery. Consequently-when the plug is inserted, a. flow of current will result from the intermediate int of battery 6 (Fig. '2), through polartzed relay 1?, normal contacts 103 and 104 to sleeve strands, plug X, sleeve run 7 of the jack F ofthc called line, cut-oil relay 16 to ground; thereby causing armature 1 05 of relay W to more to the left and close circuit from battery b, through supervisory relay 109, and said armature 105 to ground, whereby said relay 109 is energized and establishes the following circuit conditions :-Said relay 109 looks itself up via alternate contact 103, normal contact 104, sleeve conductor S, plu X, sleeve ring f, cutwfl' relay 16 of the called line to ground; whereby said relay 109 can only be denergized by the removal of the plug from the jack. In addition. alternate contact 103 is broken (preferably subsequent to the establislunent of its alternatecontact, although this is net necessary with the slowacting relay W) to disconnect polarized relay In addition, alternate contact 102 is closed to illuminate supervisory lamp 110 by current from battery b, through said lamp, normal contact 111 and said alternate contact 102 to ground. Said indication remains until the called-for party respon ls by removing his-telcph -ne from its book. thereby giving a visual indication to the operator at the response of the called-for party. The opening of normal contact 102 extinguishes the calling lamp 96. Also, alternate Contact 92 is closed to extend conductor L to ground at contact 112, via alternate contact 78, undue-tor L, normal contact 91, conductor L, alternate contact #2 and normal contact 112: thereby maintaining the busy condition of the selected link-circuit, and throwing its point or control under the influence of relay 4 4. Also, contact 113 is closed to extend alternately the tip conductor of the called subscribcrs line, first, to the ringing generator Q, and second to the tip supervisory relay 114, depending upon the position of the armature 11' of relay 41 n w under the control of the interrupter R, as described. Ringing current (from the proper source Q) is thus intermittently extended to the bell of the called subscribers line via tip strand T, alternate contact 18 of his cut-oll relay. line limb L, condenser 2, hell 1, line limb L alternate contact 17 of his cut-oil relay (one return path to ground being provided through said cut-oil relay), jack contact I, plug X, sleeve conductor S, normal contact 104, alternate contact 103, supervisory relay 109 to battery and ground. The said hell I at the called subscribers station will thus intermittently rin and the tip conduct-or will be intermittent y andalternately extended to the tip supervisory relay 114. whereby, when said subscriber removes his telephone from its hook and the armature 41 of relay 41 is in its normal position, a closed path for the flow of current from battery 6' will be established via 'supervisory relay 109, alternate contact 103, normal contact 104, sleeve conductor S, line limb L transmitter 3, olarized relay 7 (if the called subscriber he a coin-box subscriber} to ground at normal contacts 9 and .10; the current through said polarized relay 7 being of a direction to immediately cause its armature to move contact-. 9 to its alternate position and thereby continue the flow of current via said polarized relay 7, alternate contact 9, armature 8,line limb L, tip conductor T. contact 113, normal contact 41',

through said tip supervisory relay 114 to round. The removal of the telephone from its hook at the called station will,therefore, operate polarized relay 7 (if it he a coin-box subscriber) to establish the talking circuit through said station and tocausethe operation of relay 11 4 at the central oilicer If the called subscriber-were notprov-ided with a coin-box set, but were providedwith a set such as shown either at B or C, the removal of the telephone frdm" its book would di' rectly close the circuit through said relay 114 to cause its operation. with any arrangement of apparatus at the called station, therefore, the removal of the telephone energizes relay 114, resulting in the following circuit changes: Contact 115 is closed to continue the sleeve strand S from the calling to the called subscriber, normal contact 111 is broken to extinguish the supervisory lamp (thus ratifying the operator of the response by the called party) and alternate (:rntart 111 is closed to extend current from battery 6. through relay 44 and said alternate contact 111 to ground at alternate c ntart 102. whereby said relay 4! is energized to effect the following circui changes: Contact 11 is closed to lock the said relay 44 via it winding and said contact 116 through said alternatecontact 102 to ground, whereby said rvlay 41 can only be released by the removal of the plug from its jack. Also,

armature 45 is attracted and restores the de' pres ed ringing button p to its intermediate or indicating position, as previously described, simultaneously opening connection to the ringing generator Q and interrupting the circuit of relay 41 at contact 42, thereby preventing the further attraction of its armature 415 In addition, conductor L is extended via alternate'contact 112 to counti said relay 28 and contact 97' to mg magnet 51 and battery 6 of reversed po tential; A closed path for the How of current is thus Etablished from said batteryb, via counting magnet 51, alternate contact 112, alternate contact 92, mal contact 91, conductor L, alternate contact 78, conductor L, wiper?5 (Fig. 1), normat contact 76, polarized relay 9? and contact 117 to ground, thereby energizing the said counting magnet 51 and the polarized relay 97. The direction of flow of current from battery 6, through said polarized relay 97, is such as to close contact 97, thus'energizing magnet 28' from battery I), through ground. Relay 28' attracts its armature 28 to dose circuit from the battery 6 of relatively high potential, through the polarized relay 7 at the calling subscribers station over the following circuit: battery 6, said contact 28 wiper 25, line limb L, contact 9' through said polarized relay 7, transmitter 3, line limb L, alternate contact 178ml cutofi' relay 18 to ground. This flow of current is in a direction opposite to that previously flowing through the said polarized relay 7 at the subscribers st to draw arm 13 to the right thus depositing. the coin in chute 15 as previously described. Reverting to counting magnet 51',-it will be seen that, upon the complete attraction of its armatules, it will step ratchet-wheel 52 one step to register one additional completed 7 a; the substation that current in the former direction to again complete the conversational circuit via line lim L'-'. transmitter 3, said relay 7. alternat contact 9. armature S. and line limb L. The con-rersutivual circuit is thus completed hetwren'thc calling and the called subscribers the coin has been collected and deposited, and the counting magnet 51 in the linlc circuit has recorded the completed connection on the counter U. The circuit of said tion and of greater value. It will therefore elevate armature'8 and engage'arm 11, causing the extension 12 current {due to the short circuit counting magnet 51 is under the control of relay 44, which relay is locked up under the control of relay 109, which latter relay can only be denergized when the plug X is removed. from the spring-jacln whereby the movement of the hook-5 at, either the calling or. the called subscribers station can have no effect either upon the counter U or upon the collecting magnet 28.

During conversation, the calling subscriber has under his individual control the supervisory lamp 118. Said lamp, as usual.

will be illuminated by the calling subscriber conductor L, norreplacing his telephone upon its book, thereby-including said lamp in circuit from battery I), pilot supervisory relay 119, said supervisory lamp 118, contact 120, normalcon tact 93 to ground. Pilot'superrisory lamp 119' is at the same time lighted, due to the energization of the common pilot relay 119. Similarly, during conversation; the supervisory lamp llOisunder' the individual control of the called subscriber and will light when the said subscriber replaces his telephone upon hook; the circuit thus es tablished being that previously traced. Upon the conclusion of conversation and lamp 96, normal .Icontaet 91. normal contact 92, conductor L, normal :contacf 91, conductor L alternate contact 78, conductorLggolarized relay 9?, contact 11'? to groun This flow of current energizes relay 9? in a direction opposite to its previous energizationwhen included in circuit with battery 6, whereby its contact 9T isclosed to effect release as follows: A flow of current from battery b is first established via lamp 0, contact 97 relay 1:21 to ground thereby energizing said relay 121 to extend battery 7) via lamp 0, contact- 1252, release relay 19.3 and contact 117 to ground thereby energizing said relay 1:23. The cnergization of said relay 1-23 est-ab lishcs an additional path for the flow of current from battery b',,via private relay (i5. alternate contact 7T, said relay 123, to the said contact 117 and thence togro11nd,whereby said private relay 68 and said release when both subscribers hare replaced their 80 at contacts 73-74 preparatory to release, and in addition, opens normal contact 76,

whereby polarized relay 97 is released and ergized from pulsating or alternating source 9, via said magnet 21, contact 69 and can tact 70 to ground, thereby causing the continued rotation of the said link-circuit selector switch until it reaches its zero or normal point. When this point is reached, relays 68 and 123 are deenergized b the opening of contact 117, due to the re ease of relay 81, caused by the opening of H15 circuit at normal switch contact 36. All apparatus has thereforeresumed' its normal position. The wipers of the line selector H remain in enga ment with the contact points assoelated with the last subscriber calling. During the release, as above described, it is apparent that contact 101 of relay 123 will be continuously closed whereby the ground is maintained on conductor 109 of a pair of switches not in their normal position and hence not ready to receive new calls. Upon the denergization of relay 68, alternate contact 88 will be opened, thereby interrupting the circuit through cutoil' relay 16 of the calling line to again operatively connect the calling apparatus belonging to that line to the 881d line.

Second, called line busy.-If the called line be busy, the sleeve rings f of the jacks F will be at a potential difi'ernt from-the,

ground and always as great as or greater than one half the potential of battery b. This arises from the following conditions: If the busy line he one that is then initiating a. call, battery 6' (Fig. I, Part 2) may be momentarily closed through the cut-0E relay 16, via lamp 0, normal contact 87, alternate contact 88, conductor 8 including contact 83, wiper 24, conductor 3, and said cut-05 relay 16 to ground. The resistance of lamp 0 will not be greater than the resistance of relay 16, whereby the potential in the circuit above traced, at s, electrically connected to riot be less than onei the sleeve rings f will half the potential of b. As soon as selection is completed, battery I) (Fig. 2) is closed through said cut-off relay 16, via relay 89, S, wiper 80. normal contact 88, 5' including contact 83, wiper 2i, conductor 8, where the current divides, a part returning to the ground side of battery 5' via the cutoff relay 16, and :1 part continuing over the subscribers circuit and back through If, wiper 25, t including contact 84, contact 73, wiper 79, conductor T to ground throu hrelay 9U (Fig.2). The joint" resistanceo the cut-0E alternate contacts 87 and 88, conductor 8 including contact 83, wiper 24, conductor a,

where the current divides, a part returning 7 via cutoff relay 16, and a part continuin over the subscribers circuit 'and bac through it, wiper 25, t' including contact 84, contact 126, relay 121 to ground. The resistance of 54 is relatively low and the potential of battery 6 relatively high with respect to 5, whereby the potential of the rings (connected to the intermediate points a of e above circuit) will not be less than one-half the potential of battery 6'. It might of course be much greater. In case the busy line he one which has been connected to at a jack F, then its cut-oil relay 16 would be operated by current from battery 5 (Fig. 2), via relay 109, alternate contact 103, normal contact 104, conductor S, plug X, jack F, sleeve ring f, where the current divides, one part returning via cut-ofi relay 16, and the other continuing over the less than the resistance of relay 109, whereby the intermediate point f (the said sleeve rings) isniaintainedat apotential not less than one-half of battery L. It is obvious that should the busy subscriber replace his telephone onits hook, it would increase the potential of the test rings f to a value nearer the total potential of b. of a busy line, this relation between the po tential of the test rings .f and battery 6' holds true-that is, the said rings f are at a.

potential not less than one-half the potential In all conditions 119 of b. It therefore necessarily follows that the insertion of the plug X into a jack of the busy line will cause a flow of current through relay W in a direction opposite to the flow previously traced when the plug was inserted into the jack of an idle line. The flow may be traced as follo s: Starting with either the source b or L, and following either one of the various paths above traced in detail until the conductor 8 is reached, the current will continue via the test ring f of the jack into which plug X is now inserted, said plug X, sleeve conductor 5, normal contact 104, normal contact 103, said polarized relay \V, to the intermediate point of battery b. It will be remembered that said intermediate point is preferably about one-quarter the total potential, thus leaving, as a minimum effective potential for the operation of IV, a potential about one-quarter of the total potential of b. Armature 105 of said polarized relay W will therefore move to the right and close circuit from battery b, through busy relay 106 and armature contact 105 to ground, whereby said relay 106 will be energized to establish the following circuit conditions: Said relay will lock itself up from battery 6' via contact 107 and contact 108 of relay 89 to ground, whereby its release is dependent upon the release of relay 89; said relay 89 is locked up by current flowing from battery I) through said relay, alternate contact 104, sleeve conductor S, sleeve ring f of the j ack, cut-ofi' relay 16 of the busy called line to ground; whereby the release of both relays 106 and 89 is placed under the control of the inserted plug. In addition, polarized relay IV has its circuit opened at' normal contact 104, thus releasing and restoring its armature. In addition, contact 124 is closed to energize relay 44 from battery 6 via said magnet winding and said contact 124, to ground; whereby the release of said relay 44 is also placed under the control of the inserted, plug. The operation of said relay 44 cannot at this time extend battery 5 via counting magnet 51 andalternate contact 112 to the conductor L, because (the called line being busy) relay 109 then is denergized. It is, therefore, impossible at this time to either operate the counting magnet 51 at all, or to operate the relay 97 in a direction to collect the coin at the subscribers station. Moreover, it is impossible to extend ringing current to the busy subscribers line because of the open contact 113 now existing. It is also apparent that with the exception of a possible single slight click, due to the re-adjustment of the current in the busy called line at the time relay W caused relay 89 to be locked up via the cutofl" relay of said busy line, no disturbance of the called line will result; it being apparent that the conversational circuit of the selected link-circuit now connected with the calling line is interrupted at said contact 113 on the tip side and at contact 115 on the sleeve side.

The operation of relay 106 has also extended current from battery I) to polarized relay 97 via the following circuit: said battery b, the upper portion of the Winding of relay 44 (preferably of relatively low resistance), conductor 125, alternate contact 91, conductor L alternate contact 78, conductor L, wiper 75, said relay 97, and contact 117 to ground. The said relay 97 is therefore energized in a direction to close its contact 97 and to operate relay 121, which in turn, causes the energization of rescribed),

lays 68 and 123, as previously described. It Will be observed, however, that relay 121 will not in the present case, be released by the opening of contact 97 at the time relay 68 is energized, but will, on the contrary, be locked up over the calling subscx'ibers line via the following circuit: high voltage battery b alternate contact 87, alternate contact 88, conductor 8, wiper 24, line limb L, transmitter 3, polarized relay 7, alternate contact 9, line limb L, wiper 25, conductor t, contact 126, said relay 121, to ground. The heavy flow of current from high voltage battery 5 will cause the complete downward attraction of armature 8 to engage arm 11 and cause arm 12 to move arm 13 to the left, thereby releasing the coin 10 to the subscriber via chute 14. Arm 13 will therefore be free to slide through the projection 12 and allow contacts 9-10' to return to their normal positions; but as armature 8 maintains the circuit condition above traced through the relay and transmitter, the said circuit conditions will be maintained. In addition to the return of the coin, the subscriber is notified of the busy condition of the line by a flow of current from the busy back apparatus N (previously devia condenser 40, contact 127, conductor t, wiper 25, line limb L, the calling subscribers telephone set, line limb L, alternatecontact 17 and to ground through cut-0d relay 16, or the other ground returns then present. The subscriber is thus advised that the desired line is busy, his coin has been returned, but the link selector I has not as yet returned 'to normal, owing to the continued energization of relay 121, due to the assumption that the calling subscriber has not as yet replaced his telephone upon its hook.

Referring again to the linkcircuit (Fig. 2), it is apparent that relay 90 has been released bv the opening of contact 73 of relay 68 (Fig. 1), thus causingthe illumination of supervisory lamp 118 (and pilot supervisory lamp 119') over the circuit previously traced, and that supervisory lam 110 is now illuminated over the fol lowing path: battery 6, said lamp 110, normal contact 111, contact 116, contact 124 to ground, whereby the operator receives the complete disconnecting signal. In other words, the instant the operator inserts the plug into the jack of a busy line, she receives the com lete disconnecting signal, entirely irrespective of whether or not the calling subscriber replaces his telephone upon its hook. The calling subscriber meanwhile has been advised that the called line is busy. The operator in obedience to the disconnecting signal removes the plug from the jack, thus unlocking relay 89 and restoring the entire link-circuit apparatus to its normal position. It is apparent that the energization of relay 44 and its subsequent denergization 

